The present invention relates to a print control device for color print and a printing method, and particularly to a print control device and print control method in which printing is performed by a two-step print head which has printing elements of each color for color print, each row of the printing elements being arranged in a longitudinal direction of the print head.
In color print by a printer (printing apparatus), various colors are expressed by combination of cyan (C), magenta (M), yellow (Y), and the like. As a color used for a character, black (K) is also used. Therefore, a print head includes printing elements for printing these colors. Though there is also a printer which includes elements for other colors than these colors, since the basic principle is the same, the description in this specification is performed using these four colors.
For example, in an ink jet printer, in order to eject these four kinds of ink, four kinds of ink ejection nozzles directed to each color of CYMK are required. There are print heads in which ejection nozzles for each color of CYMK are provided line by line longitudinally, and a print head in which ejection nozzles are provided in an upper area and a lower area so that the upper area and the lower area have two colors respectively (referred to as a two-step print head). The print head is mounted on a carriage moving transversely, and when the carriage moves on a printing paper traversely, the ejection nozzles of the print head mounted on the carriage eject necessary ink onto the printing paper so that color printing is performed.
For example, in a print head in which ejection nozzles for each color of CYMK are provided line by line longitudinally, that is, four rows of ejection nozzles are provided in total, when the print head traverses the printing paper once (referred to as a “print pass” where the carriage thus traverses the printing paper), the ejection nozzles for all the colors pass through the same position of the printing paper. Therefore, by one print pass, color printing is completed.
However, in the two-step print head in which the ejection nozzles for CYMK are provided in the upper area and the lower area so that the upper area and the lower area have two colors respectively, the ejection nozzles for all the colors of CYMK cannot pass through the same position of the printing paper. Therefore, in order to print the four color data, a print pass for printing by upper-step printing elements and a print pass for printing by lower-step printing elements are required (two print passes are required in total).
FIG. 15A shows an example of a two-step print head 70. In the two-step print head 70 shown in FIG. 15A, a nozzle group 71 of C-color and a nozzle group 72 of Y-color (lower-step nozzle groups) are arranged on the lower step side of the two-step print head longitudinally, and each nozzle group includes 32 nozzles. A nozzle group 73 of K-color and a nozzle group 74 of M-color (upper-step nozzle groups) are arranged on the upper step side longitudinally, and each nozzle group includes 32 nozzles. FIG. 15B shows a printing process (print pass) for a color print by the two-step print head 70 in the related art.
When a printing paper 81 moves from the downside to the upper side (the print head moves from the upside to the downside: in a Y1-direction), in order to complete the color printing of the height corresponding to 32 picture elements, in a first print pass (1), first C-color printing and Y-color printing are performed by the lower-step nozzle groups. Next, after the printing paper has been moved so that the upper-step nozzle groups pass through the same position as the position in the first print pass, in a second print pass (2), K-color printing and M-color printing are performed by the upper-step nozzle groups. In this second print pass (2), the lower-step nozzle groups execute a first print pass for printing the next print data. Thus, by the two print passes, printing for all the colors of CYMK is completed (The print pass in which printing is completed is shown by oblique lines in the upper step of the two-step print head 70). When the two print passes are thus executed, the print data are assigned to both of the upper-step nozzle groups and the lower-step nozzle groups.
Further, in a related art, print data hear the page end is printed by the printing element located upward of the original printing element thereby to prevent a platen from being stained with the ejected ink (refer to JP-A-2002-172771 and JP-A-2002-172772).
However, the print data are assigned to both of the upper-step printing elements and the lower-step printing elements in order from the upper side printing element, and when the print data near the page end is printed by the upper-step printing elements, the printing paper must be fed near the upper end of the upper-step printing elements (refer to a last print pass “L” in FIG. 15B). By this paper feeding, the lower-step printing elements can move to the upper side of a print starting position of a next print page 82. In this case, in order to print the print data of the next print page 82 by the lower-step printing elements of the two-step printing head correctly, after the printing paper has been transported in the opposite direction (Y2-direction), printing of the next printing page 82 must be started. Transportation in the opposite direction (reverse feeding) not only makes a paper feeding mechanism complicated but also causes deterioration of print quality due to delay of print speed and backlash.